This invention relates to an air inlet system of a small-sized engine for use in a portable working tool such as a chain saw, a bush cutter, and a blower fan.
FIG. 1 shows a conventional small-sized engine of the type described. A carburetor 7 is fixedly connected to an air inlet 3 of an engine cylinder 1 through a heat insulator pipe 5. A suction port 9 of the carburetor 7 communicates with an atmosphere through a filter 11. In a chain saw, for example, the suction port 9 of the carburetor 7 communicates with an atmosphere through a gap between a handle 13 and a carburetor cover 15, or a gap between a fuel tank 17 integral with the handle 13 and the carburetor 7.
Generally, a portable working tool often produces dust such as chips, sawdust, and sand dust. In the conventional engine, air is directly sucked from an atmosphere into the carburetor 7 through the filter. In this event, the sucked air inevitably contains a large amount of dust which is stuffed into the filter. This requires frequent cleaning of the filter. Thus, maintenance of the filter is troublesome.